Oxygen Sensor Heater Test -P0141 (2.2L Chevy S10, 2.2L GMC Sonoma)

Testing the 4-wire rear oxygen sensor's internal heater on your 2.2L Chevy S10 (2.2L GMC Sonoma) is a piece of cake.

So, if your check engine light is lit by a diagnostic trouble code (DTC) P0141: HO2S Heater Circuit Sensor 2 on your 2.2L Chevy S10 (2.2L GMC Sonoma) in this tutorial I'll show you the 3 basic tests you'll need to perform to find out.

You don't need a scan tool (although having one is a big plus). All you'll need to follow this tutorial is a multimeter.

NOTE: This oxygen sensor is known by several different names:

  1. Downstream Heated Oxygen (O2) Sensor.
  2. HO2S Sensor 2.
  3. Rear Oxygen (O2) Sensor.
  4. Oxygen Sensor Bank 1 Sensor 2.
  5. Oxygen Sensor After the Catalytic Converter.
  6. Post-Catalytic Converter O2 Sensor.

Here are the contents of this tutorial:

  1. Circuit Descriptions Of The Downstream Oxygen Sensor.
  2. TEST 1: Verifying The Heater Element Is Getting Power.
  3. TEST 2: Verifying The Heater Element Is Getting Ground.
  4. TEST 3: Testing The Heater Element's Resistance.
  5. Where To Buy The Oxygen Sensor And Save Some $$$.
  6. More 2.2L GM Diagnostic Tutorials.

Circuit Descriptions Of The Downstream Oxygen Sensor

Oxygen Sensor Heater Test -P0141 (2.2L Chevy S10, 2.2L GMC Sonoma)

If you've already done any kind of research on the rear oxygen sensor (on your 2.2L S10 or Sonoma) you know it's a 4 wire heated oxygen sensor.

To effectively test the rear O2 sensor, we need to know what these wires do. In a nutshell, 2 of the 4 wires are for the oxygen sensing part of the sensor. The other two wires feed power and ground to the O2 sensor's heater element.

Below, you'll find the color of the wires of the engine wiring harness oxygen sensor connector for the rear oxygen sensor:

Downstream Oxygen Sensor Pinout
(2.2L Chevy S10 - 2.2L GMC Sonoma)
Pin Wire Color Description
A TAN/WHT O2 Signal Ground
B PPL/WHT O2 Signal
C BLK Heater Ground (-)
D PNK Heater Power (+)

TEST 1: Verifying The Heater Element Is Getting Power

Oxygen Sensor Heater Test -P0141 (2.2L Chevy S10, 2.2L GMC Sonoma)

The first test we'll do is to make sure that the pink (PNK) wire of the engine wiring harness oxygen sensor connector is feeding the rear O2 sensor with power.

Power is in the form of 12 Volts (from a fuse in the fuse block) and to verify that it's reaching the rear O2 sensor we'll do a simple multimeter voltage test.

CAUTION: The oxygen sensor tests must be done with a completely cold engine. Since the O2 sensor is bolted to the exhaust pipe... it gets and stays very hot (even after engine shut down)! Be careful and take all necessary safety precautions! If you raise your vehicle with a jack, place it on jack stands!

IMPORTANT: The pinout in the illustration above is of the connector on the oxygen sensor itself. To check for power, you need to test the PINK wire of the engine wiring harness sensor connector.

OK, this is what you'll need to do:

  1. 1

    Locate the downstream oxygen sensor and disconnect it from its harness connector.

  2. 2

    Locate the PNK wire of the engine wiring harness oxygen sensor connector.

  3. 3

    With your multimeter in Volts DC mode, probe the BRN with the red multimeter lead.

    Ground the black multimeter lead directly on the battery's negative terminal.

  4. 4

    With the Key On Engine Off (KOEO), the PNK wire should have 10 to 12 Volts DC.

Let's take a look at your test results:


CASE 1: The PNK wire is feed the rear O2 sensor with 10 to 12 Volts DC- Good, since this confirms that the rear oxygen sensor's heater element is getting power.

The next step is to make check that the black (BLK) wire, of the O2 sensor engine wiring harness connector, is feeding ground to the heater element. For this test, go to TEST 2: Verifying The Heater Element Is Getting Ground.

CASE 2: The PNK wire IS NOT feeding 10 to 12 Volts DC to the rear O2 sensor- Re-check that you're testing the correct wire and that the Key is in the RUN position (but don't crank or start the engine) and re-test.

If you still don't see 10 to 12 Volts DC... then this test result tells you that the downstream oxygen (O2) sensor itself IS NOT BAD... since without power, the heater element won't work.

Although it's beyond the scope of this article... the next step is to find out why this battery power is missing using a wiring diagram.